By definition, we can say that corners and penalties are free kicks. But, the qualities requires to take different free kicks are different. Someone good at crossing the ball can take free kicks and corners, but he can still have difficulty taking some free kicks because of the wall, the distance and the power of the shot needed and so on. A corner specialist will definitely have good crossing ability, while a free kick specialist will need good shooting ability as well.
But for a penalty, the main qualities that you need here is decision, calmness, shooting power and accuracy, which all are needed for one-on-ones. What one-on-ones need in extra is acceleration and control (which both can be put as one - dribbling) so that the player can round the goalkeeper to score if needed.
Speaking of abilities, I think that a player should not be limited to only one ability. There are so many players in real life that had more than 1. For e.g, Thierry Henry and Andrea Pirlo had 4, Lionel Messi And C. Ronaldo have at least 2, D. Beckham and Ryan Giggs had 2.